The major focus of the project is the investigation of renewal mechanisms in rods and cones, and in the pigment epithelium, of the vertebrate retina. We are using radioisotope-labeled precursors, including acetate, amino acids, monosaccharides, and various lipid precursors labeled with tritium. These are injected into experimental animals (rats, frogs, ground squirrels, goldfish), or are used to label isolated retinas in vitro. The location of the labeled molecules is subsequently determined by conventional and electron microscope autoradiography. During the coming year, particular emphasis will be placed on projects designed to help elucidate the nature of the differences between rods and cones in the mechanism of formation and renewal of outer segment membranes.